In mixing two fluids together to create a mixture with the amount of a first fluid precisely controlled, normally a fluid delivery device is needed for metering and delivering the first fluid into a second one. Metering methods in the fluid delivery apparatus include a pump metering method, in which a metering pump is used to precisely control the amount of the first fluid to be delivered, and a common rail method, in which the first fluid is contained in a common rail or a buffer chamber with its pressure controlled higher than that of the second fluid, and the metering is achieved by controlling the open time of a nozzle fluidly connected to the common rail. To mix the two fluids uniformly, in delivering the first fluid into the second one, typically the fluid delivery device needs to have the first fluid atomized into small droplets. In a fluid delivery apparatus using the common rail method, since the pressure in the common rail can be controlled high, a good atomization can be achieved with small nozzle orifice and high common rail pressure. In a fluid delivery apparatus with metering pump, however, since the metering pump is for controlling delivery amount of the first fluid, delivering pressure is not controlled. To have a good atomization, normally a third fluid, e.g., a compressed air is used to assist atomization.
An example of such a fluid delivery apparatus is a reductant delivery apparatus in an exhaust gas treatment system of an internal combustion engine. Environmentally harmful species in the exhaust gas emitted from an internal combustion engine, such as hydrocarbons (HC), carbon monoxide (CO), particulate matters (PM), and nitric oxides (NOx) are regulated species that need to be removed from the exhaust gas. In lean combustion engines, due to the existence of large amount oxygen excess, passive means without extra dosing agents, such as a three-way catalyst apparatus used commonly in spark-ignition engines, normally are not able to effectively remove the oxidative specie NOx. To reduce NOx in lean combustion engines, a variety of active means with reducing agents (reductants) being dosed in exhaust gas are developed. In these technologies, the reductant is metered and injected by a fluid delivery apparatus into the exhaust gas, and the result mixture flows into a SCR (Selective Catalytic Reduction) catalyst, where the reducant selectively reacts with NOx generating non-poisonous species, such as nitrogen, oxygen, carbon dioxide, and water.
To have a fine atomization, in the fluid delivery apparatus, normally the first fluid is sprayed into the second fluid. This type of fluid delivery creates a difficulty in measuring actually delivered amount of the first fluid in the second fluid. Another difficulty in measuring actually delivered first fluid is caused by the harsh environment in the second fluid. For example, in an exhaust gas treatment system, the second fluid is exhaust gas, which has high temperature and contains high moisture, particulate matter, and possibly reactive gas species, such as NOx, SOx, and CO. In such an environment, it is difficult to position a normal flow sensor in the second fluid. The lack of sensing means that is able to measure the actually delivered first fluid results in that the delivery accuracy relies on the performance and reliability of the delivery components in the fluid delivery apparatus, since errors caused by the delivery components cannot be compensated in system level. For example, in an apparatus with common rail control, pressure control performance, nozzle orifice size, and nozzle opening control performance determine delivery accuracy, and the metering pump control performance is the major factor affecting delivery accuracy in a fluid delivery apparatus with pump metering if there is no feedback compensation.
Furthermore, in applications where the first fluid is a liquid and the second fluid is gaseous, sometimes the first fluid needs to be evaporated in the second fluid. For example, in a SCR exhaust gas treatment system, the first fluid is a urea solution. It needs to be evaporated in the second fluid, which is exhaust gas. In the evaporation process, if the second fluid is not able to provide enough thermal energy, then the first fluid may condense and cause issues. In the example of the SCR exhaust gas treatment system, when the urea solution condenses on exhaust pipe, it may polymerize and crystallize, forming solid deposits, which may grow and eventually block exhaust flow.
To solve these problems, it is then a primary object of the present invention to provide a fluid delivery apparatus with a flow rate sensing means that is able to detect the actually delivered amount of the first fluid in the second fluid. The sensed flow rate is then used in a feedback control to adjust delivery rate in system level.
A further object of the present invention is to provide a fluid delivery apparatus with an evaporation sensing means, which generates sensing values indicative to the evaporation capability of the first fluid in the second fluid. The evaporation sensing values are then used in determining the maximum allowed delivery rate so that only evaporable first fluid can be delivered into the second fluid.
Another object of the present invention is to provide a multifunctional sensing means in a fluid delivery apparatus using the common rail method. The multifunctional sensing means is able to provide the flow rate of the first fluid, evaporation sensing values, and other sensing values including the temperature of the second fluid and the flow rate of the second fluid.
Yet another object of the present invention is to provide a diagnostic means in a fluid delivery apparatus using the information obtained from the multifunctional sensing means and other sensors to monitor the operating status of the fluid delivery apparatus and report faults when an abnormality or an error is detected.
Yet another object of the present invention is to provide a regeneration means for the sensing means in a fluid delivery apparatus. The regeneration means removes the deposit of the first fluid on the sensing means to avoid sensing errors.